Space Security Service agent Marc Cory arrives covertly on Kembel. Cory
and his team are on a mission to uncover the plans of the Daleks and their
intergalactic allies, who are secretly meeting on the planet. But Kembel
is a world of many dangers, and as his companions slowly transmute into
deadly Varga plants, Cory soon realises that for him, there is no
escape.

Production

In October 1964, Head of Serials Donald Wilson ordered that the opening
story of Doctor Who's second season, Planet Of
Giants, be trimmed to three episodes from four due to a perceived
lack of dramatic impetus. At the time, it was suggested that the Dalek
story planned to be made at the end of the second production block (which
would later be abandoned and replaced with The
Chase) might be expanded from six episodes to seven as
compensation. Nothing came of this.

Nonetheless, it was likely because of the loss of the fourth Planet Of Giants episode that, around the start
of 1965, Head of Drama Sydney Newman extended the second recording block
from twenty-six episodes to thirty-five, rather than a more obvious
allotment of thirty-four. By this time, Doctor Who stories were
being made exclusively in either four or six parts, and so the addition of
nine episodes to the schedule would force a deviation from the usual
pattern.

The extra episode would be the first to feature neither
the Doctor nor any of his companions

At around the same time, Terry Nation was completing work on The Chase. Keen to repeat the success of the
transmission of The Dalek Invasion Of Earth
during the Christmas 1964 period, producer Verity Lambert and story editor
Dennis Spooner asked Nation to contribute another six-part Dalek story for
broadcast around November and December 1965. In tandem with this, it was
decided that the extra episode remaining at the end of the recording block
could be used for a special “trailer” for this new Dalek
adventure. To save on the cost of contracting the regular cast for the
additional installment, this would be the first Doctor Who episode
to feature neither the Doctor nor any of his companions. Nation was
commissioned to write this one-off, given the title “Dalek
Cut-Away” and the production code DC, on February 25th.

The popularity of the Daleks by this stage was so great that Nation was
beginning to mull the possibility of a Dalek spin-off programme, perhaps
even one which could be exported to the United States, a market Doctor
Who had so far failed to crack. He therefore viewed “Dalek
Cutaway” (as the episode became known) as an opportunity to lay the
groundwork for such a show. As such, Nation developed the concept of the
Space Security Service (also called the Special Security Service and the
Space Special Security Service) and Agent Marc Cory, whom Nation conceived
as a “space-age James Bond” (building on the popularity of the
Bond movie franchise, recently spiked by the release of
Goldfinger). The Service would later feature prominently in The
Destroyers, Nation's unmade 1966 pilot script for his proposed Dalek
series.

“Dalek Cutaway” was originally set on the planet Varga. Around
July, the name was altered to Kemble and then Kembel. The Varga plants
themselves retained their original name, but now became artificial
creations of the Daleks, brought to Kembel from Skaro, as opposed to a
natural, indigenous form of life. The alien delegate Zephon was deleted
from the script, presumably due to financial concerns. Also in July, the
name Mission To The Unknown was applied to Nation's script
although, confusingly, the “Dalek Cutaway” title would also
continue to be used in some documentation. (Indeed, some sources suggest
that Mission To The Unknown is the title of the single episode
which makes up a serial called “Dalek Cutaway”.) Rather than
leading into a standard six-part Dalek story, it was by now known that
Mission would serve as a prologue for an unprecedented
twelve-episode adventure called The Daleks' Master
Plan.

Mission To The Unknown was
made by the same crew as Galaxy 4

Due to its unique nature, it was decided that Mission To The
Unknown would be made by the same crew as had been assigned to the
previous story in production, Galaxy 4 (Serial
T), including director Mervyn Pinfield. Filming at the Ealing Television
Film Studios would also be carried out for the two adventures
simultaneously. Because of this -- as if the confusion over its title
wasn't enough -- Mission would henceforth also be referred to as
Serial T/A, Serial Ta, and even “Serial T Episode 5” in
addition to the previously-assigned Serial DC.

Although the filming dates assigned to Galaxy
4 and Mission To The Unknown spanned June 22nd to 26th, the
brevity of the latter meant that it would only be featured on the schedule
for the final day. By this time, Pinfield had fallen badly ill and had to
be replaced at short notice by novice director Derek Martinus; Pinfield
would retire from television soon afterward, and passed away in the
mid-Sixties.

With Martinus at the helm, Mission enjoyed its lone studio session
on Friday, August 6th in TC4 at the BBC's Television Centre (a change from
the originally-planned TC3). Recording of the episode itself was preceded
by the enactment of the final scene of Galaxy
4's concluding installment -- the cliffhanger into Mission
-- which had been held back to avoid having to both hire actor Barry
Jackson (Garvey) for two weeks and erect the Kembel set an extra time. The
completion of Mission also brought Doctor Who's second
production block to a close.

By the time Mission To The Unknown was taped, Spooner had already
left Doctor Who to be replaced as story editor by Donald Tosh.
Lambert, too, had all but handed over the producer's reins to John Wiles,
and this would be her final credited serial: a photocall was held on the
day of recording to mark the end of her involvement in Doctor Who.
Lambert would go on to produce a number of critically- and
popularly-acclaimed programmes, including The Newcomers, Adam
Adamant Lives! (which, like Doctor Who, was created by Sydney
Newman), Quatermass, Minder and Jonathan Creek. She
became the Controller of Drama for Thames Television in 1979, and in the
Eighties formed her own production company, Cinema Verity. Lambert was
awarded the Order of the British Empire in 2002; she passed away
following an illness on November 22nd, 2007.